Portable devices such as laptop computers, cell phones, pagers, personal digital assistants, and the like require a self contained power source such as a rechargeable battery, e.g., lithium, nickel-cadmium, or nickel-metal hydride batteries, to facilitate the portable nature of such devices. One exemplary portable device, a laptop computer, is now a common tool for many travelers given there increasingly expanding capabilities and uses.
A docking station couples to a laptop computer in one easy connection to make it more convenient to use a laptop computer in a desktop environment. The docking station may, in turn, be coupled to a variety of peripheral devices such as a full size keyboard, a mouse, disk drives, a full size CRT monitor, a printer, and others. Therefore, a laptop user may make one simple connection, instead of many, to a docking station and have access to a host of peripheral devices not typically available in a laptop computer.
Both conventional laptop computers and docking stations are typically equipped with charging circuits or chargers. A laptop charger provides charging current to charge the laptop's rechargeable battery or batteries. Similarly, the docking station provides charging current to charge the docking station's rechargeable battery or batteries.
Such laptop chargers and docking station chargers typically have two current sensors, e.g., resistors that are located close to the input and output ports of the chargers. Such sensors are located in closed proximity to the chargers because the involved signals are relatively small and easily perturbed. A first current sensor is located close to the input port of the charger and serves to sense the input current from an associated power supply. A second current sensor may be used to control charging current output from the charger. For example, a resistor may be used for both sensors because by monitoring the voltage drop across a known resistor, the current level can be ascertained.
Such chargers may also include a current allocation circuit known to those skilled in the art. Such a circuit receives a sensed signal from a sensor close to its input ports representative of the current provided by the associated power supply. The circuit may then vary charging current provided to the batteries based on the maximum level of supply current available from the power source. For instance, if the maximum level of supply current available from the power source is reached, the current allocation circuit may reduce the charging current for the batteries in order to maintain the current level from the power supply within its maximum tolerance level.
When a laptop is docked on a docking station, the docking station typically provides the power for both the laptop and the docking station. In this instance, if the laptop charger is charging the laptop's battery or batteries, it needs information about the total current delivered by the docking station's power supply in order to keep it within its maximum current supply limits. In order to do this, it is known to send all the power from the docking station to the laptop via an associated conductor and connector in order for the laptop supply sensor to sense such current supply levels.
It is then also necessary to send-back to the docking station sufficient power required by its circuitry via another conductor and connector. As such, the associated conductors and connectors need to have high current carrying capability. Higher current levels also translate into higher power losses as well. In addition, when both current sensors on the input side of the laptop charger and docking station charger are resistors, the current path from the docking station to the laptop and back to the docking station encounters such resistors in series which further increases power losses.
Accordingly, there is a need in the art for a portable device and docking station that have charging circuits with remote power sensing capabilities.